Main window won't change
Simply change that top toolbar back to Info.  That's the default for Blender.  From there you have all the traditional menus.  From the Info bar, you can select your preferred Workspace.  You can use the Motion Tracking Workspace which is already setup with three Movie Clip Editor panes or you can create your own custom Workspace:



As far as I know, the top bar is the only one you cannot pull down down into a pane (like all the other panes):